So having made the leap to get my instrument completely overhauled (as in everything taken off, cleaned, wood treatment, new springs, pads, tone holes, adjustment, the works), I borrowed someone else's clarinet. It is an Evette and Schaeffer in top shape, and it plays wonderfully. Notes just respond better, the upper register pops out easily, and it is better in tune than mine.

Can I expect mine to come back in similar condition? I have an R13 that has had regular service, pads as needed, etc., but I honestly don't think I ever had a complete overhaul done before. It is a 1977 horn. I don't want to get my expectations too high. Have your full overhauls restored the instrument to the point that it responds and tunes much better than before?

I am also getting the keys replated due to a nickel allergy, so it will be gone for a month and a half, so I have a lot of time to get used to the other instrument and don't want to be disappointed after spending all that money.

Quite clearly a full overhaul should always make an instrument play and respond better than it did just before the overhaul.

A really fine overhaul from a really competent tech should make your instrument play at least as good as it did when new.
With the best techs and typical manufacturer's less than perfect quality control then it is should be quite possible for your instrument to actually play even better than new.

However silk purses out of pigs ears is unrealistic, so if your instrument was not one of the best output then don't necessarily expect it would come back as "artist" quality

I actually asked the tech (who specializes in clarinets, is used by several professionals and comes highly recommended) about my instrument. He said I have a decent R13. Unfortunately we were pressed for time when I dropped it because he had another appointment coming shortly, so he only had a chance to play it quickly to make an assessment. I have had it since I was a teenager, went to Interlochen on it and moved to the first part in every band I have been in since so I assume it isn't a complete dud of an R13. My expectation is it will be a "really fine overhaul from a really competent tech." But at age 14 I don't know that I knew what I was doing when I picked it out and I certainly didn't have it "set up" at the time. I just broke it in and played on it.

My Buffet R-13's came back from the Brannen's with significant improvements in response and feel after an overhaul.

My Yamaha CSG's came back from Lohff & Pfeiffer after I had played them a lot for about eight years with only basic maintenance, and I was just stunned at how well it played at every single dynamic level after the overhaul. The action was completely silent, the response of the keys was noticeably better, and to top it off it came with a 3-year warranty on the work so minor updates didn't cost me anything except getting it into Wolfgang's hands wherever he was traveling in the US at the time.

John Butler has done fantastic overhauls on a number of instruments for my students...they come back like they are new clarinets!

Competent techs don't just get the clarinet back to spec, they improve aspects of the mechanism, intonation, and response, according to their aesthetic.

With a quality overhaul from a tech that is adept at tweaking intonation and response, a Vito Resotone or B&H 10-10 can play better than most new, professional clarinets (with the possible exception of Yamahas, which are set up reasonably well). The setup and attention to detail is at least as important as the provenance...in many cases more so. Buffet R-13s can be nice clarinets, but for decades now they have been delivered with a huge variety of dimensional and setup variation...an R-13 that has never had a professional setup can be profoundly better when returned from a competent overhaul.

Tuning is not affected by an overhaul, unless of course there is a lot of dirt inside the tone holes. If pads or dampers are replaced, the pad heights and the venting capacity of the tone holes can be different. But that kind of adjustment can and should be done continuously.

Fixing leaks will not affect the tuning. I have made tunings tests with terribly leaking pads, and then fixed the problem and made tests again. If a leaking instrument tunes terrible it will tune as badly when it is air tight.